162 Microscopic Histochemistry 



First of all, neither the enzyme*^^ nor the aldehyde formed 

 ( p-hydroxyphenylacetaldehyde ) is insoluble enough to re- 

 main at its original site; both would diffuse out into the solu- 

 tion. Second, the oxidation of tyramine by amine oxidase 

 goes beyond the aldehyde stage^^- ^^ unless the aldehyde 

 formed is promptly trapped (e.g., by semicarbazide ) . 



In addition to the theoretical objections, it can be shown 

 experimentally that positive reactions are obtained even in 

 the absence of substrate and after the treatment of the sec- 

 tions with chemicals which almost certainly destroy the 

 enzyme (trichloroacetic acid). *^^ 



The chemical nature of the aldehyde giving the peculiar 

 blue shade with Schiff's reagent is not known, but it appears 

 to be either a modified form of plasmal or some other lipid 

 aldehyde produced from unsaturated fats by nonenzymatic 

 oxidation. It is not likely to be an aromatic compound, such 

 as would be formed by enzymatic action, because the shades 

 given by simple aromatic aldehydes are much more reddish. 



c) PEROXroASES 



Enzymes of the peroxidase group catalyze the transfer of 

 oxygen from hydrogen peroxide and other peroxides to a 

 variety of acceptors. Chemically, most if not all of the perox- 

 idases appear to be heme proteins. They are quite resistant 

 to various chemical and physical agents, especially to acids 

 and heat. 



It must be remembered that some substrates may be at- 

 tacked by peroxides (not necessarily all peroxides) directly^^ 

 and that some of the catalysts are not of pyotein nature ( iion 

 porphyrins; in some instances even inorganic Fe salts in con- 

 junction with ascorbic acid).^^ Therefore, a reaction obtained 



65. Blaschko, H., Richter, D., and Schlossmann, H.: Biochem. J., 31:2187, 

 1937. 



66. Bemheim, M. L. C: J. Biol. Chem., 93:299, 1931. 



67. Gomori, G.: Ann. New York Acad. Sc, 50:968, 1950. 



68. Dixon, M.: Biochem. J., 28:2061, 1934. 



69. Bezssonoff, N., and Leroux, H.: Bull. Soc. chim. biol, 28:286, 294, 

 608, 1946. 



